Traffic nightmare: The new normal for the rainy season?

On Monday, June 17, thousands of motorists were affected by extreme traffic along major thoroughfares in Metro Manila. 

Only a month in to the Philippines’ typical rainy season, the question is: How extreme was the rainfall on Monday to have caused the traffic chaos? 

Public and private commuters spent hours on EDSA and on C-5 only to ply a few kilometers, with some even giving up and walking in the rain. Some reported the experience similar to being trapped in a parking lot.

Many attributed the cause for traffic to be the rains and the subsequent floods brought by Tropical Storm Emong.

Is Monday’s extreme traffic the new normal for the rainy season?

Heavy rain in southern Metro Manila

The Manila Observatory (MO), a private, non-profit Jesuit research institution, owns several weather stations in Metro Manila. MO operates and manages the Metro Weather network of Automated Weather Stations (AWS) and is a part of the Makati City Network of AWS. The Metro Weather network is a partnership between MO, Chevron, Globe Telecommunications, Ateneo de Manila University and the Metro Manila Development Authority (MMDA).

Data gathered from the AWS were used to collect information on the rainfall on Monday. Data from the AWS showed that rain fell more heavily in the southern part of Metro Manila. San Juan recorded a total rainfall accumulation of 114.6 mm. Among the network of weather stations, West Rembo, Guadalupe, Navotas, Tayuman and Payatas also recorded the highest accumulated rainfall in the Metro (see Table 1). The MMDA has pegged 50 mm as an hourly-accumulated rainfall threshold for floods to occur in flood-prone areas.

Based on the results of the analysis, Metro Manila received the most rain from around 3:00 pm to 8:00 pm. During that period of time, San Juan received up to 63 mm of rain per hour. The heaviest rain was concentrated between 5-7 pm, where San Juan received 105 mm total in two hours.

For reference, during Tropical Storm Ondoy (Ketsana) in 2009, a total of 270 mm fell in a period of six hours as recorded at the Manila Observatory, with a peak rate of 61 mm per hour. Ondoy dropped a total of 370 mm of rain in a period of 24 hours.

Figure 1a shows the hourly rainfall accumulation rates for the stations that received the highest rainfall in Metro Manila. Payatas received over 40 mm of rain between 4:30-5:30 pm but little rain after this period. San Juan received the most amount of rainfall concentrated in about one hour, between 6:30-7:30 pm. Guadalupe and Tayuman, Manila also received most of their rainfall during this hour while Las Piñas experienced the most rain between 7:30-8:30 pm. This progression of heavy rain shows that the rain pathway moved southward (Figure 1b).

Impact on traffic

Data showed that there was heavy rainfall in various parts of Metro Manila especially between 6:30-8:30 pm. MMDA reported that traffic was most snarled along parts of EDSA and C-5. MMDA has listed a number of flood-­‐prone areas along EDSA: Balintawak, North Avenue, Aurora Boulevard in Quezon City, Connecticut and Shaw Underpass in Mandaluyong, Ayala Tunnel and Pasong Tamo Tunnel in Makati City and Taft Avenue and Harrison in Pasay City. MMDA has also listed parts of C-­‐5 that are vulnerable to flooding.

Cars were at a standstill at C-5 near Tiendesitas and the EDSA-Ortigas area due to impassable floods. MMDA reported flooding in other parts of the Metro such as the Blumentritt and Biak na Bato areas. The RMB Pureza area was also reported to be flooded.

The time of the heaviest rainfall coincided with rush hour, when most motorists and commuters were on the road to get home. According to the data from the weather stations, there was scant recorded rainfall before 3:00 pm in the Metro, so the ground and other pathways for the rain to flow were not necessarily saturated before the downpour. The sudden and heavy fall of rain within only a few hours accumulated quickly and caused floods. The runoff may have also overwhelmed local drainage canals and waterways. This, along with other factors such as slope, obstructions or construction on the road, also may have contributed to the flashfloods and caused several choke points along the flood-prone areas along EDSA and C-5.

The MMDA information on flood-­‐prone areas and Monday night’s flooded areas were combined to produce a map of the flooded areas vis-à-vis the points with heavy rainfall (Figure 2), with emphasis on EDSA, C-5 and Quezon Avenue. The high rainfall recorded at Tayuman station matches the cause for the reported flooding in Blumentritt and the Biak na Bato areas. Rainfall in areas towards Mandaluyong, Makati and Pateros may have affected EDSA between Ortigas and Guadalupe.

The heavy rain concentrated in a few hours – particularly during the peak traveling time – was a major cause of the congested thoroughfares on Monday night. Rainfall was heavy due to the regular monsoon season and enhanced by the presence of Emong in the Philippine Area of Responsibility.

Accumulated rainfall from 5:00-8:00 pm, combined with MMDA flood-prone areas along EDSA and C-5 and reported impassable roads.

New challenges to roads, infrastructure, commuters and motorists

The Philippines has an average of 19 tropical cyclones (depressions, storms, typhoons) every year that enter the Philippine area of responsibility and especially during the monsoon season until December.

However, as many Filipinos now realize, it doesn’t take a typhoon to create traffic chaos anymore. “Regular” monsoon rain events, such as the Habagat and Monday night’s rainfall, show that Metro Manila faces new challenges each rainy season.

According to the Intergovernmental Panel on Climate Change (IPCC), climate change may also change precipitation patterns, creating “new normals” of heavy and intense rainfall, thus making extreme events more frequent. The rainy season is predicted to be much wetter than previously experienced, which poses real challenges to the public roads and infrastructure.

In a megacity like Metro Manila, the risk of traffic chaos is high when combined with heavy rainfall, a high volume of cars, vulnerable roads and few alternatives to major thoroughfares. Similar to Monday night, the heaviest rain can pour at peak travel times and many motorists may be trapped for hours in bad traffic as a result. Climate change threatens to make these situations worse because of the potential for more extreme rain.

It is crucial for the Philippines to engage in timely and efficient monitoring of the weather and road conditions and disseminating accurate information to the general public.

This was first published at the Manila Observatory’s official website. Republished with permission.